Ocean Audio Archive

Signature Three

The Ocean Audio Signature Three is no longer manufactured.
Interphase Audio NDUCR is the new and improved version.

The information on this page is for reference only.

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The Signature Three is no longer available.
While being one of the best-sellers in the Ocean Audio range of products, the Signature Three was not designed by Malcolm Toft, but by Allan Bradford.
The Interphase Audio NDUCR (19”) or Iridium (500 series) are designed by Allan Bradford and are the new and much improved versions of the Signature Three.

Signature Three
Dual Channel, All Discrete, Inductive Equaliser

The Signature Three consists of two identical channels of discrete transistor - inductor based - equalisation. Silicon transistors as opposed to integrated circuits (op-amps) provide a much simpler dedicated signal path, thereby providing a much cleaner signal path. Silicon transistors can also be run at much higher voltages than integrated circuits which vastly increases the headroom capability.

Inductor based circuits are the ‘holy grail’ of equaliser designs. These were used for example in the much favoured Pultec equaliser design, which dates back to the late 1950‘s. Owing to their unique electro-mechanical properties, inductors impart a character all their own which is very distinctive. Because of their cost and large size, inductors are rarely used in the low frequency ranges of other currently available equalisers. Most other manufacturers use non-inductive, shelving circuits for the extreme low and high ranges, but these circuits do not give the precise control provided by inductors.
The Signature Three uses inductors in each of the four sections (bands) giving precise control and the distinctive inductor sound on each range.

Each range provides switch selection of any of six carefully selected frequencies chosen at musically pleasing intervals. Each range is also provided with a continuously variable cut and boost control allowing a maximum of plus or minus 15dB. A centre detent offers instant return to the ‘neutral’ position.

As mentioned above, the Signature Three uses inductors in each of the four sections and as a consequence provides a ‘peaking’ characteristic. This provides much tighter control of the frequency selected and the inductor values and components have been carefully chosen and matched to provide an extremely musical sound. One example is Signature Three's ability to enhance bass frequency signals without introducing the unwanted 'boom' so often found in many modern equaliser designs.

A feature of the design made possible by the use of individual transistors is the ability to handle high signal levels with very low distortion. The Signature Three is capable of providing output signal levels in excess of +28dBm which could overload the equipment that is connected to the output. To provide a visual indication when the output signal is approaching a level that could cause problems, a large LED illuminates when the signal at the output exceeds +15dBm.

Because the Signature Three only uses individual silicon transistors, the noise and frequency response of the unit is to a very high specification. With the equaliser section bypassed, the noise in the bandwidth 20Hz to 20kHz is below –85dBm. With the equaliser in circuit and all boost/cut controls in their centre position, the noise in the bandwidth 20Hz to 20kHz is below –80dBm.

The precision components used in the design and manufacture of the unit guarantee close matching between the two channels. This means that the Signature Three can be used as a mastering device when accuracy between the two channels is extremely important.

When the equaliser is switched out of circuit (‘IN’ button out), the equaliser circuitry is completely bypassed thereby ensuring the best possible signal to noise ratio and a minimum of electronic circuitry in the signal path.

The Signature Three combines the very best of classic equaliser design with modern day technology and components.

The Signature Three is no longer available.
The Interphase Audio
NDUCR (19”) or Iridium (500 series) are the new and much improved versions of the Signature Three.

Some of the highlights of the Signature Three :
* All discrete Inductive Equaliser
* Two independent channels
* Four bands per channel with switchable, overlapping frequencies:
- Low : 50, 80, 100, 150, 300, 600 Hz
- Low mid : 125, 250, 500, 1K, 2K, 4K Hz
- Hi mid : 2.5, 3, 5, 6, 7, 8 kHz
- High : 8, 9, 10, 12, 14, 16 kHz

* Hand-crafted and hand-wired by Ocean Audio in the UK


Technical Specifications

Input impedance (Jack and XLR) : > 15K ohms electronically balanced
Output Impedance (Jack and XLR) : < 100 ohm electronically balanced
Frequency Response : ± 1dB 15Hz to 35kHz
Maximum Output level : > +28dBu at all frequencies Equaliser in or out
Distortion at +4dBu output : < 0.005% THD
Distortion at +27dBu output : < 0.05% THD
Noise EQ out : < -85dBu (20Hz - 20kHz)
Noise EQ in : < -80dBu (20Hz - 20kHz)
Gain : 0dB ±0.5dB Equaliser in or out
Nominal Operating Level : 0dBu
Power requirements : 80 volts - 260 volts

The Signature Three is no longer available.

The Interphase Audio NDUCR (19”) or Iridium (500 series) are the new and much improved versions of the Signature Three.

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Signature Three


Click image to download file
PDF file - 2.9 MB

From our archive

Newton Abbot - October 2014
Malcolm talks you through the Signature Three

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April 2015 - KMR Audio reviews the Signature Three

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January 2015 - Sound on Sound magazine publishes a nice review of the Signature Three

"There is something very attractive in the sound character of inductor-based equalisers that's hard to describe - they just sound more natural and 'right' to my ears, especially at the bass end of things. ... Overall, this is an unusual inductor-based dual-channel equaliser with all-discrete transistor circuitry that delivers a classy and attractive sound, with well-sorted EQ options"
(SOS, January 2015)

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